Users of mobile telephones and smartphones often communicate using techniques other than voice communications. For example, Short Message Service (SMS) is a text messaging service, using standardized communication protocols, that provides for the exchange of short text messages between fixed line or mobile telephone devices. SMS may be used to send text messages between end-users of mobile telephones and/or fixed line devices. Additionally, SMS may be used to provide text messages from online applications or services to users. For example, a user may sign up (“opt-in”) to be alerted, via a text message, when an event occurs that is relevant to the user (e.g., a weather service may send a text message alert when severe weather is forecast for a particular area).
Some services, that are provided via text messages, may allow users to initiate and terminate the service by texting particular keywords to an SMS address. For example, the keywords “start” and “stop” may commonly be used to indicate that a user would like to start or stop a particular service. In this situation, a user may text “start” to a desired shortcode (a special telephone number that is shorter than a full telephone number) to start a service. Subsequent text messages for the service may come from the shortcode. The user may text “stop” to the shortcode to end the service.
Network providers, such as a cellular network operator, have an interest in ensuring that the users of the network only receive text messages from sources authorized and/or desired by the users. Users that receive a large amount of unwanted text messages may be dissatisfied and tend to blame the network provider.